Gas discharge flash lamp circuit



March 5, 1963 P. HOEKSTRA 3,

GAS DISCHARGE FLASH LAMP CIRCUIT Filed Sept. 3. 1959 16 z 5 3 5 L C INVENTOR PIET HOEKSTRA AGEN 3,080,562 GAS DISCHARGE FLASH LAMP CIRCUIT Piet Hoekstra, Ernntasingel, Eindhoven, Netherlands, as-

signor to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Filed Sept. 3, 1959, Ser. No. 837,831

Claims priority, application Netherlands Sept. 25, 1958 Claims. ((11. 315-476) The invention relates to a device known from US. Patent No. 2,829,315, issued April 1, 1958, comprising an electric light source in the form of gasor vapourfilled, artificially cooled high-pressure discharge lamp, which is energized by pulses via controlled, gasor vapour-filled relay valve in order to obtain light flashes. Such a device may be employed, for instance, in a picture film projector, in which the projector lamp emits one or more light flashes per film picture. The relay valve is controlled by means of electric pulses via the grid so that it conveys current during the flashing period, whereafter in the normal operational conditions the current is interrupted. The current pulses thus produced traverse also the projector lamp, which is thus caused to emit light flashes. This process may be repeated with a frequency determined by the frequency of the pulses.

In accordance with the invention the discharge lamp is energized, in addition, by a direct-voltage source, so that it is continuously traversed by a rest current.

Owing to the presence of the said rest current the lamp does not ignite again at each pulse, since the lamp remains ignited, be it invis-ibly.

This provides the advantage that the puls-atory supply voltage for the lamp, controlled by the relay valve, may be materially lower.

As stated above, it is common practice with such a device to cool the high-pressure discharge lamp artificially, for example, with the aid of water. Since the relay valve, supplying the discharge lamp, is not ignited during the starting period of the projector (about 2 sec.) the discharge lamp then does not produce flashes. The rest current, however, is switched on by starting the projector motor. As soon as the latter and also the projector have reached the desired speed, the relay valve is ignited periodically. It has been found, however, that, if the starting period is too long, the rest cur-rent (of for example 0.1 to 0.5 A.) already switched on produces such a high temperature of the tungsten electrode that it is volatilized, so that a black deposit is produced on the wall of the lamp.

This disadvantage is obviated in accordance with a further aspect of the invention by providing the driving motor of the projector with a low-power generator, from which a positive voltage can be obtained, which is supplied to the control-circuit of an adjustable rectifier, which, however, remains blocked during the start of the motor by a negative control-voltage and which serves to energize a relay, the contacts of which interrupt the circui-t of the rest cur-rent and the pulse during the start. When the projector motor has attained its full speed of revolution, the positive voltage derived therefrom is so high that it compensates the negative cu-t-ofi voltage to an extent such that the rectifier ignites and the contacts are closed.

A further aspect of the invention consists in that the voltage of the generator is supplied, in the form of synchronized ignition pulses (for instance by means of the striking pin of the Maltese cross of the projector) to the relay valve. During the start the voltage of these ignition pulses is not yet sufliciently high to ignite the relay valve, which may give rise to the aforesaid blackening of the wall of the lamp.

From the above-mentioned US. patent it is known that aforesaid interruption of the current in the normal operating condition sometimes does not occur owing to the relay valve remaining conductive after the termination of the flashing period, which gives rise to an abnormal operating condition in which a continuous current is maintained and the effect of the use of the light flashes is lost.

The disadvantages brought about by this abnormal operational condition are avodied in a device according to the said U.S. patent by including in the circuit of the relay valve and the light source a relay switch, whic can be switched on and off by a controllable rectifier with the aid of a control-voltage, obtained from an impedance included in the circuit and having such an effeet on the rectifier, after the device has been switched on, in the normal operating condition in which the relay valve is periodically conductive, that the switch is closed, Whereas in the case in which, after the termination of the flashing period, the relay valve remains conductive, a control-voltage is produced whereby the switch interrupts the circuit.

According to a further aspect of the invention the last-mentioned device is employed in that the cut-off vlotage and the positive ignition voltage are supplied to the said controllable rectifier, so that the latter is used for two purposes.

The invention will be described more fully with reference to the drawing.

The FIGURE shows a device comprising a high-pressure mercury-vapour lamp 1, which is supplied, in order to obtain a plurality of light flashes, via a controlled, gasfilled relay valve 2. The lamp 1 is cooled by means of a water system, which is not shown in the FIGURE for r the sake of simplicity. The device is energized by means of a direct-voltage source 3, which feeds a capacitor 5 via a resistor i. This capacitor will be discharged through the relay valve 2, the projector lamp 1 and the coil 6, when the circuit thus formed is closed by the switch 13 and the relay valve 2 conveys current. At such a discharge a damped LC-oscillation is produced, which produces a flash current in the projector lamp. Since during the next-following half period of the oscillation the polarity of the voltage across the relay valve 2 is different, this valve will be non-conductive and thus prevent further oscillations. This process may be repeated, since after some time, the relay valve again becomes conductive by a pulse at the grid 7, so that the capacitor 5, which has been recharged in the meantime, can again produce a damped LC-oscillation, which again gives rise to the emission of a single flash. In the normal operational conditions the relay valve must convey current only during the flashing periods, whereas beyond these periods no current must be passed.

As stated above, there is a risk of a continuous passage of current through the relay valve 2 after the circuit has been closed. In this case the capacitor 5 is no longer charged in addition and the lamp 1 will be directly energized from the source 3 via the relay valve 2. This condition is stable, since the damped LC-oscillation is lacking and there is no cause for the relay valve 2 to be blocked. The circuit of the valve 2 and the lamp 1 includes a mechanical switch 13, which can be switched on and ofi by a control-voltage, which is derived from a resistor 9 in the circuit, which resistor is connected in series with the lamp 1. The relay 8 is energized from the alternating current supply voltage via a transformer 12 via a controlled rectifier, which comprises two gas-filled tubes 10 and 11, whilst the control via the interconnected grids is obtained by the control-voltage from the resistor 9. The supply circuit of the relay 8 includes, moreover,

to the fact that during the flashing period the tubes and.

1-1 are cut all by the control-voltage, so that during this time the relay is not fed, which does not afi'ect the total mean time owing to the arrangement of the relay and toy theshort duration. However, if in the abnormal operational conditions an abnormal current occurs owing to the relay valve remaining conductive, the resultant control-voltage will give rise to such a reduction in the mean relay current that the switch 13 is released and interrupts the circuit. Thus the control-voltage is suppressed. and the switch 13 is re-attracted, so that the flashing proc-.

ess can restart. This may be repeated until the normal operational conditions are reestablished. This process has so short a duration that it has no appreciable efiect on the quality of the film projection, if the light source is employed as a projector lamp in a film reproducing apparatus.

When the projector motor 15 is switched on by closing the switch 14, the direct voltage source 16 is automatically switched on, which source supplies the rest current for the lamp 1; the lamp 1 is cooled by connectingit' with the water mains by well known means not shown. The shaft of the motor 15 is coupled with the Maltese cross of the projector. (not shown), on which a pulse generator 17 is provided, which supplies pulses for the ignition of the relay valve 2 via the transformer 18.

The rectifiers 10 and 11 include screen grids 19 and 20, to which an alternating voltage from the winding 21 is fed, this voltage being in phase opposition to the anode voltage of the valves 10 and 11. The centre of the winding 21 is connected via the rectifier 22 to one terminal of the generator 17, of which the other terminal is connected to the cathodes of the valves 10 and 11. pacitor 23 and a resistor 24 serve as a smoothing device. During the start of the motor 15, the voltage produced by the generator 17, at-the transformer 18 is too lowv to ignite the valve. Even the positive bias voltage obtained by the rectifier 22 between thescreen grids 19 and and the cathodes of the valves 10 and 11, is too low to compensate the negative alternating voltage from the winding 21, so that the valves 10 and 11 remain cut off and the switch 13 remains open. Therefore norest cur rentflows from the voltage source 16 through the lamp 1.

As soon as the motor 15 has substantially attained thefull speed of revolution, the voltage of'the generator 17.

increases so that the valves 10 and llbecorne conductive and the switch 13 is thus closed, after which the relayv valve 2 also becomes conductive and the first light flash is produced in the lamp. Thus blackening of the lamp is. avoided.

What is claimed is:

1. A device comprising a light source in the form of a gaseous discharge lamp, circuit means for supplying electric pulses to said lamp thereby to intermittently energize the same at a high intensity value, means for additionally supplying a direct voltage to said lamp .thereby'to en'-.

ergize said lamp at a low intensity level, switch means-i11- terposed between said lamp and said direct voltage sup-. ply, and control means responsive to the interruption of A ca-.

the electric pulses supplied to said lamp to actuate said switch means thereby to interrupt the application of said direct voltage to said lamp.

2. A device comprising a light source in the form of a gaseous discharge lamp, circuit means for supplying electric pulses to said lamp thereby to intermittently energize the same at a high intensity value,- mean for additionally supplying a direct voltage to said lamp thereby to continuously energize said lampat a low intensity level, switch means interposed between said lamp and said pulse and direct voltage supply means, means for actuating said intermittent energizing means, and means for closing said switch. means after a given interval following theinitiation of the operation of said actuating means.

3. A device comprising a light source in the form of a gaseous discharge lamp, circuit means for supplying electric pulses to said lamp thereby to intermittently energize the same at a high intensity value, means for additionally supplying a direct voltage to said lamp thereby to continuously energize said lamp at a low intensity level, switch means interposed between said lamp and said pulse and direct voltage supplymeans, means for actuating said intermittent energizing means, and means for closing said switch means after a given interval following the initiation of the operation of said actuating, means, said closing means comprising an electron discharge system for energizing said switch means, means for biasing said discharge system in a deenergizing condition, and mean responsive,

to said actuating means for overriding said biasing means.

4. A device comprising a light source in the form of a gaseous discharge lamp, circuit means for supplying electric pulses to said lamp thereby to intermittently energize the same at a high intensity value, comprising.

agaseous discharge relay valve, means for additionally supplying a direct voltage to said lamp thereby to continuously energize said lamp at a low intensity level, switch means interposed between said lamp and said pulse and direct. voltage supply means, means fior actuating. said relay valve comprising a source of triggering pulses recurring at a given periodicity, said source being connected to said relay valve, and means for closing said switch meansinterposed' between said lamp and said;

pulse and direct voltage supply means, means for actua ting said relay valve comprising a source of triggering pulses recurringat a given periodicity, said source beingv connected to said relay valve and means'for closing said' switch means after a given interval following the initiation of operation of said source of triggering pulses, said closing means comprising an electron discharge system fior energizing said switch means, means for biasing said discharge system in a deenergizing condition, and means responsive to said actuating means for overriding said biasing means.

References Cited inthe'file of this patent UNITED STATES PATENTS 1,908,191 Schriever May 9, 1933 2,178,423 Inman .Oct. 31, 1939 2;385,397 Blackburn Sept. 25, 1945' 2,829,315 Hoekstra Apr. 1, 1958' 

1. A DEVICE COMPRISING A LIGHT SOURCE IN THE FORM OF A GASEOUS DISCHARGE LAMP, CIRCUIT MEANS FOR SUPPLYING ELECTRIC PULSES TO SAID LAMP THEREBY TO INTERMITTENTLY ENERGIZE THE SAME AT A HIGH INTENSITY VALUE, MEANS FOR ADDITIONALLY SUPPLYING A DIRECT VOLTAGE TO SAID LAMP THEREBY TO ENERGIZE SAID LAMP AT A LOW INTENSITY LEVEL, SWITCH MEANS INTERPOSED BETWEEN SAID LAMP AND SAID DIRECT VOLTAGE SUPPLY, AND CONTROL MEANS RESPONSIVE TO THE INTERRUPTION OF THE ELECTRIC PULSES SUPPLIED TO SAID LAMP TO ACTUATE SAID SWITCH MEANS THEREBY TO INTERRUPT THE APPLICATION OF SAID DIRECT VOLTAGE TO SAID LAMP. 